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satanskin
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Joined: 25 Apr 2005
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 Posted: Thu Nov 17, 2005 2:43 am Post subject: Move to Nforce4 Raid |
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Alright so I have a few questions about the nforce4 raid and just raid in general.
Background info: I currently have Gentoo installed and working the way I like it. I have 2 raptors and my partition scheme for the Gentoo install is:
sdb1 /boot
sdb2 /swap
sdb3 /
So for the questions, I would like to move this install over to a RAID0 across the raptors. What would you suggest as the best way to do so without losing/killing this install and having to start over? Also, is it possible to raid only a partition rather than an entire drive? For example to raid only the / partition? Or to Raid0 / and Raid1 /boot as mentioned in this thread https://forums.gentoo.org/viewtopic-t-400021-highlight-nforce4+raid.html ? The last I heard, GRUB wouldn't work on a raided drive. Does this still apply or how do you get around this?
I found this program called dmraid here http://people.redhat.com/~heinzm/sw/dmraid/ has anyone used this before? Will it migrate the current install over to the raid and setup the software raid? I know there was a program that came with my old computer in windows that allowed me to pick the disks, setup the raid, and then it would do that and migrate the OS install to the array. This worked even when using the drive the OS was installed on already. Does this make sense and is it possible somehow in linux? Thanks in advance. |
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mudrii
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satanskin
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| Posted: Thu Nov 17, 2005 5:20 am Post subject: |
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| But how could I move my current install over to a RAID? I don't want to have to reinstall from scratch and all those articles/guides are about installing from scratch. |
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mudrii
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| Posted: Thu Nov 17, 2005 7:28 am Post subject: |
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One possibility to make stage 4 backup after make RAID partition just unpack stage 4 backup.
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Zanfib
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satanskin
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| Posted: Thu Nov 17, 2005 3:45 pm Post subject: |
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This is rather informative, but seems to be talking about moving from one physical disk to another. I have sda and sdb with gentoo installed on sdb. I want to raid0 sda and sdb together and have that gentoo install striped across the array. I guess the stage4 back up and then untarring it seems like it is going to be my best option so far. Thanks guys! |
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satanskin
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| Posted: Thu Dec 08, 2005 10:50 pm Post subject: |
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Ok, so Grub doesn't work on a RAID0. Now is that grub itself that can't be striped? Or just the boot partition? Meaning could I do the following:
rda1 /boot
rda2 swap
rda3 /
where rda is the RAID0 array of my two raptors and GRUB is installed to the MBR of /dev/hda? I mean will it still be able to pick up the files from a striped array inorder to boot and just can't be installed, itself, to one? Or can it not even read from the striped array? If this IS possible, anyone have a suggestion on how to setup the grub.conf for that? |
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deepspace9
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| Posted: Fri Dec 09, 2005 12:08 pm Post subject: |
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You can use nvidia raid stuff if you use dmraid and the kernel device mapper! Works just fine for me, althought I'm still not sure about the performance.. but since this is just default linux raid 1, this could very well be a sata problem..
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barbapapa
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Joined: 27 Jul 2005
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| Posted: Fri Dec 09, 2005 3:13 pm Post subject: |
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my opinion:
i use dmraid on my two raptor raid (stripping), simply put, it was paintfull since you need the 'last' (when i do it on july) version (dmraid before this is buggy on nvidia) and no live cd was ok (the only with dmraid was outdated and has no reiser4, you can found it somewere on the gentoo forum) . dmraid is the only way to use (with soft raid) with a windows partition. since the 2 two disk is see as a one you need to set grub 'by hand' (block mode) (sorry you will have to found the link i don't remener where is the faq but you could found it). you must too use a specifique initrd (well that easy use "genkernel --dmraid all" in fact with th md module in)
it's clearly not that easy, myself has use another disk and i use a copy part to part (you can use 'tar' or 'cp -i-don't-rembenber-the-option') i don't think you can do differenty... no easy direct option...
"from what i know" if you only use a linux you should not use dmraid and use the linux raid since it's purely logicial you can put each partition with a specifique setting i don't think there is a point to set /boot on a raid array. /boot must/should be the simpler possible, in ext2, it is 'never' more than 100M since it's only use on 'early' boot (get the initrd and the linux kernel) so you gain prety nothing with an array (100M in a raptor...) exept probleme... |
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barbapapa
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| Posted: Fri Dec 09, 2005 3:17 pm Post subject: |
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| i too think you should considere to not simply use a / partition at least use a /home partition. (personalty i use / /usr /var and /home and a tmpfs for /tmp). just my opinion... |
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HackingM2
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| Posted: Fri Dec 09, 2005 6:18 pm Post subject: |
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| satanskin wrote: | | Ok, so Grub doesn't work on a RAID0. Now is that grub itself that can't be striped? Or just the boot partition? |
Can I point out that grub would be perfectly capable of working of any RAID level you like as long as it was supported by the BIOS.
The reason that it can and will only ever work on RAID 1 is that the BIOS is incapable of booting from anything else.
When the machine first boots the BIOS checks to see if there is a MBR in the first sector of the first drive. If there is then it looks up the start address of the boot loader (grub in this case) and runs that. If the boot partition was striped then how would the BIOS know where to look? This is why RAID has to be level 1 for the boot partition (and why each drive should have the same MBR and be made bootable) unless it is implemented in hardware in which case it appears to the BIOS as one drive anyway. |
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garlicbread
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| Posted: Wed Dec 21, 2005 9:21 pm Post subject: |
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something to be aware of with grub and Bios raid
the drive numbering is different depnding on where your looking from
inside the Linux OS grub sees each disk individually (since Linux doesn't use the Bios to see the disks)
e.g. inside linux
hd0 -> Raid 0 member1
hd1 -> Raid 0 member2
hd2 -> Raid 1 member1
hd3 -> Raid 1 member2
at Bios bootup it uses the Bios to detect the disks instead of Linux
hd0 -> entire Raid0 Array
hd1 -> entire Raid1 Array
something to bear in mind when setting up grub.conf
in otherwords grub on Raid 0 should be possible as grub will be reading the kernel and initramfs files via the Bios initially which takes account of the striping
you just have to make sure that you install it onto the /dev/mapper/nvidia_xxx device and not hd0 hd1 etc within linux (as that would be the individual raid members not the array)
EDIT
Just spotted this on another thread, though I'd post it here
inside the grub prompt
teach grub that (hd0) and (hd0,0) are not individual disks
| Code: | device (hd0,0) /dev/mapper/${devicename_of_your_bootpartition}
grub> device (hd0) /dev/mapper/${devicename_of_your_raid} |
now install
| Code: | grub> root (hd0,0)
grub> setup (hd0) |
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deepspace9
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| Posted: Thu Dec 22, 2005 2:34 pm Post subject: |
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That's exactly how it goes
Can anyone tell me something about the performance of dmaid? I'm not sure it's very good, since I really have no good reference comming form a SCSI only system  I did some bonnie++ tests and wasn't very impressed with it.. can post some results later:
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garlicbread
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| Posted: Thu Dec 22, 2005 4:45 pm Post subject: |
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I think it's the performance of device-mapper within the kernel
dmraid will just setup a device-mapper mapping the same way you can with dmsetup (it's just easier to use )
I've got a really old thread over here
with a graph / picture at the bottom using zcav from my old mobo
it seems to be definitely better for Raid 0 as the Linux software Raid seems to plateau out to a straight line after a certain point
dm raid 1 vs Linux software Raid 1 looks to be roughly the same
(although you do have the advantage of dual booting with Bios / dm raid) |
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deepspace9
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| Posted: Fri Dec 23, 2005 8:21 am Post subject: |
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Hmm, so it could also be the performance of the Sata driver in the kernel.... My Sata raid 1 is significantly slower than my old software raid 5 setup (4 10K disks).
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Gentoo on AMD64
